Modeling the Thermodynamic Properties of Common Minerals at High Temperature, Pressure and Salinity with Complex Ions

Abstract

The ultra-high temperature (150-250 o C), pressure (1,000-2,000 bar, 15,000 to 30,000 psi) and TDS (>300,000 mg/L) in deepwater oil and gas production pose significant challenges to scaling control due to limited knowledge of mineral solubility, kinetics and inhibitor efficiency at these extreme conditions. Prediction of thermodynamic properties of common minerals is currently limited by lack of experimental data and inadequate understanding of modeling parameters. In this study, a new apparatus was built to test scale formation and inhibition at high temperatures and pressures. Solubilities of two common minerals, barite and calcite, were tested at temperature up to 250 o C, pressure up to 1,500 bar (22,000 psi) and ionic strength up to 6m in solutions with elevated concentrations of mixed electrolytes (e.g., calcium, magnesium, sulfate and carbonate) representing the maximum range of interferences expected (95%CI) in oil and gas wells. As an attempt towards experimentally determining mineral solubility at high temperature, pressure and salinity, not only does this study contribute to the extremely limited data base, but it also provides a reliable approach for evaluating and adjusting model predictions at extreme conditions. Predictions by a thermodynamic model based on Pitzer's ion interaction theory were evaluated using experimental data. The dependence of Pitzer's coefficients for ion activity coefficients on temperature and pressure was examined and incorporated into the scale prediction model, whose prediction is consistent with both experimental and literature data at all conditions tested.

A Thermodynamic Model for the Solubility Prediction of Barite, Calcite, Gypsum, and Anhydrite, and the Association Constant Estimation of CaSO4(0) Ion Pair up to 250 °C and 22000 psi

“…The details of the apparatus and measurement procedures for different systems can be found in the previous papers. 15,27,65,66 Anhydrite (CaSO 4 ) and gypsum (CaSO 4 •2H 2 O) are the two stable phases of calcium sulfates and will transit between each other or other phases (e.g., hemihydrate, CaSO 4 •0.5H 2 O) depending on the supersaturation state, temperature, pressure, and water activity. 67,68 Under most conditions, the dominant and stable phase is believed to be gypsum under 40 °C, and anhydrite over 130 °C.…”

Scale Modeling in Reservoirs: a New Simulation Capability and its Validation with Field Data

“…The conditional solubility constant K sp, c is calculated as a function of temperature, pressure and water composition using an approach similar to that adopted by ScaleSoftPitzer (SSP), a scale software package developed by the Brine Chemistry Consortium of Rice University. In SSP, the activity coefficients of ions are calculated using Pitzer's ion interaction theory, and the solubility constant K sp is obtained by regression of high temperature high pressure data reported by Helgeson and others (Shi et al, 2012).…”

Modelagem Da Solubilidade Do Carbonato De Cálcio Em Condições Do Pré-Sal

“…Vale mencionar, que outro fator que afeta o cálculo do SI são os valores das constantes de dissociação do ácido carbônico (K1 e K2) e da constante de equilíbrio da calcita ( 3 ). Assim sendo, destaca-se o trabalho de Li e Duan (2007), em que os autores propuseram um modelo para o cálculo dessas constantes -o modelo vem sendo aplicado com sucesso em diversos trabalhos, como os de Shi et al , (2012), Shi et al, (2013 e Dai et al, (2014). Adicionalmente, Kharaka et al (1988) propuseram uma correlação para correção das referidas constantes cinéticas em função da temperatura e pressão, que foi satisfatoriamente validada.…”